The present invention relates to flame analyzing methods and apparatus, and particularly to a method and detector apparatus for detecting the presence and/or concentration of one or more chemical substances therein by igniting a combustible gas mixture containing the sample to produce a flame, and detecting a characteristic of the resulting flame.
Flame based detectors for gas chromatographs (GC) and air impurities are extensively utilized in chemical analysis, and constitute the major selective molecular detectors in use today. Most notable are: (a) the flame ionization detector (FID), which is the most commonly used GC detector, and which is selective for organic molecules; (b) the flame phototometer detector (FPD), which is used for the selective detection of sulfur and phosphorus containing molecules; and (c) the atomic absorption detector (AAD), which is used for trace metal analysis.
The conventional detectors of this type utilize a continuous flame produced by the continuous combustion of gasses, usually hydrogen and oxygen (alone or in air). The detected molecule, if introduced into the flame, may indicate its presence by the formation of charge carriers (positive ions, negative ions, or electrons), or by electromagnetic radiation emission, e.g., ultraviolet (UV), visible or infrared (IR). Alternatively, the combustion can create new species which are amenable to easier detection in spectroscopic techniques, such as fluorescence excitation or atomic and molecular absorption spectroscopy in the UV, visible, or IR spectral ranges. These and other flame effects are referred to as characteristics of the flame.